v=[-1 1];
o=[0 0];

ceuArrow(o,v,'b',2)
text(v(1)-0.2,v(2)+0.2,'v','FontSize',14)
axis([-2 1 -1 2])
axis square
grid on
text(-0.4,0.6,'||v||','FontSize',14)
xlabel('x_1')
ylabel('x_3')